In general, a skateboard includes a longitudinal oval plate and two sets of wheels each having two rollers mounted on the bottom of the plate. This conventional skateboard can be accelerated by a rider's stamping on the ground at the time of straightly traveling and can be steered by the rider's leaning to left and right sides at the time of turning.
However, such a conventional skateboard cannot be accelerated without the rider's stamping on the ground, but can be accelerated by only an extremely skillful rider's leaning to left and right sides in the traveling direction. When the plate is inclined to a side to some extent at the time of turning, the wheels and the plate come in contact with the ground and thus the plate has not to be inclined much. Accordingly, the radius of rotation thereof is great.
Therefore, a skateboard divided into a front board and a rear board has been recently proposed to solve such a problem. The skateboard divided into two parts includes a plate divided into a front board and a rear board, a hinge unit connecting the front board and the rear board, and casters movably mounted on the bottoms of the divided boards.
Such a skateboard divided into two parts is disclosed in U.S. Pat. No. 4,076,267, U.S. Pat. No. 4,082,306, JP-UM-A-1-117385, JP-UM-A-13-29663, and Korean Patent Nos. 394848 and 505754. On the other hand, the technique of accelerating a skateboard divided into two parts by twisting the skateboard is disclosed in U.S. Pat. No. 1,056,357 and Korean Unexamined Patent Application Publication No. 2002-28361.
The publications disclose a structure in which a skateboard is divided into two boards, the divided boards are connected by an elastic hinge unit, and casters are mounted on the bottoms of the boards. In the publications, the skateboard is accelerated by twisting the divided boards to left and right sides in the traveling direction, the hinge unit has a simple restoring force against the twist, and the hinge unit is coupled to the boards using bolts and nuts. Accordingly, it is difficult to assemble and disassemble the skateboard and thus to replace the hinge unit due to damage or the like.
Since the skateboard divided into two boards is accelerated by twisting the skateboard, the durability of the hinge unit is very important. However, the skateboard divided into two boards has a restoring force against the twist as an elastic deformation and thus the restoring force against the elastic deformation deteriorates due to the use for a long term. Accordingly, it may not become possible to drive the skateboard in a desired direction, thereby causing often disorders and destruction of the skateboard.
Therefore, there is a need for a hinge unit of a skateboard divided into two boards, which can provided a good acceleration force and highly durability against the twist and can be easily disassembled and assembled, thereby simplifying the maintenance and repair.